East Mountain is known for its extensive scenic cliffs, unique microclimate ecosystems, and rare plant communities.

The Metacomet Ridge continues north as the Mount Tom Range and south across the Westfield River as Provin Mountain.

The mountain formed near the end of the Triassic Period with the rifting apart of the North American continent from Africa and Eurasia.

Subsequent faulting and earthquake activity tilted the strata, creating the cliffs and ridgeline of East Mountain.

Hot, dry upper slopes, cool, moist ravines, and mineral-rich ledges of basalt talus produce a combination of microclimate ecosystems on the mountain that support plant and animal species uncommon in greater Massachusetts.